Two out of three unexpected hospital deaths are attributed to hypoventilation, many of which could be prevented if hypoventilation is detected earlier. During hypoventilation, as the concentration of carbon dioxide (CO2) in the patient's arterial blood rises (hypercarbia), the patient becomes increasingly susceptible to abnormal cardiac rhythms and, ultimately, cardiac arrest and death. Capnometers and pulse oximeters form the front-line safety net for detecting hypoventilation when patients have compromised gas exchange during procedural sedation, anesthesia or cardiopulmonary illness. When supplemental oxygen is being delivered, oximeters are less effective leaving capnometers to provide the only reliable real-time warning of potentially fatal hypoventilation. Thus, it is imperative that capnometers function correctly to ensure patient safety. Unfortunately, one out of every hundred incidence reports involving capnometry misreading is attributed to capnometer malfunction. These incidences could have been avoided if the functional issues had been properly detected in a timely manner.
For nearly all clinical monitors (ECG, blood pressure, etc.), clinical engineers use patient simulation devices to create precise, clinically realistic, signals against which the parameters reported by the monitor are compared. At present, there is no such patient simulation device for capnometers and anesthetic agent analyzers (a.k.a: respiratory gas monitors, or “RGMs”). RGMs function by drawing a sample of exhaled/inhaled gas from the patient's airway through tubing to the gas monitor sample inlet port, analyzing the sample inside the RGM, and then venting the analyzed sample through an exhaust port. Within a typical RGM is a sampling pump that creates negative pressure to draw the sample to the monitor through the sampling tube. Also within the RGM are valves, tubing, chambers, etc. which have the tendency to develop leaks or other malfunctions. Most of these components are typically on the sampling side (negative pressure side) of the sampling pump. Even very small leaks in the sampling gas pathway can cause ambient air to be drawn in and mixed with the sample gas, resulting in a diluted sample and, therefore, an inaccurate measurement. These leaks can be very difficult to detect, because their effect is typically calibrated out during routine calibration. However, the magnitude and effect of the leak changes with sample inlet pressure, so a monitor that appears to work normally during calibration may read inaccurately when put into use and subjected to changing pressures, such as those encountered during mechanical ventilation. As such, there are many capnometer failure modes that can only be detected under dynamic pressure and CO2 levels experienced during real patient use. Capnometer performance is currently verified using a static flow of calibration gas at ambient pressure, which is incapable of detecting failure modes that only exhibit in real-world conditions.
Given the foregoing, there is a need for a reliable gas monitor leak detection device, as well as a patient simulator that can simulate patient breath at pressures common during mechanical ventilation. Such a system will allow for the detection of additional failure modes that are currently undetectable by traditional test methods. The current disclosure seeks to solve these and other problems.